Workpiece supports for locking and supporting workpiece on a workpiece pallet, for example, have been provided for use in machining workpiece and the like. The present applicant has proposed and submitted patent applications for various workpiece supports (also referred to as hydraulic locking devices) (see Japanese Utility Model Application Laid-Open Nos. S59-128902, H6-47710, and other publications), particularly workpiece supports with a simplified structure.
The workpiece support with a simplified structure is provided with a rod, a sleeve body that is externally fitted on the rod and is elastically deformable so as to shrink in diameter, a case member for supporting the sleeve body, a scraper externally fitted on the rod and retained by the leading end of the case member, for scraping debris adhering to the external peripheral surface of the rod when the rod is retracted, an external peripheral hydraulic chamber formed on the external periphery of the sleeve body, and a hydraulic cylinder for moving the rod in the axial direction; and the like.
When workpiece is supported by this workpiece support, the workpiece is set on top of the workpiece support, and oil pressure is supplied from an oil pressure supply source to a hydraulic operating chamber. Whereupon, a rod-moving hydraulic cylinder is actuated, the piston member of the hydraulic cylinder moves upward, and the rod advances upward by the urging force of a compression coil spring held on one end by the piston member. The output part at the leading end of the rod lightly contacts the workpiece with an extremely small force.
As the hydraulic operating chamber of the hydraulic cylinder is then connected with the external peripheral hydraulic chamber via an oil passage, oil pressure is developed in the external peripheral hydraulic chamber on the external periphery of the sleeve body, the sleeve body is elastically deformed so as to shrink in diameter to firmly lock the rod, and the workpiece is supported by the rod. The urging force of the aforementioned compression coil spring must be pre-set extremely low in this workpiece support in order for the rod to be firmly locked after the workpiece is held lightly without elastic deformation occurring in the workpiece.
However, in the conventional workpiece support, fine shavings and dust adhering to the surface of the rod and fine shavings and dust scraped off by the scraper penetrate into the apparatus through the small gap between the rod and the scraper and adhere to the internal surfaces of the scraper and sleeve body, particularly when the rod is retracted. In this case, the sliding resistance of the rod with the sleeve body increases, the rod ceases to advance smoothly, and mechanical failure occurs. Specifically, because the urging force of the compression coil spring for moving the rod upward is extremely weak, smooth advancing movement of the rod is impeded by the sliding resistance between the rod and the sleeve body. Durability also decreases markedly as the rod and sleeve body are roughened and caused to rub against each other.
Furthermore, as fine shavings and dust adhere to the internal surface of the scraper, cutting oil on the surface of the rod more easily penetrates into the apparatus. Because the workpiece support is configured such that the rod is locked by friction acting between the rod and the sleeve body, when cutting oil penetrates between the rod and the sleeve body, the friction acting between the rod and the sleeve body decreases, and the support functionality of the workpiece support declines. In this case, during machining, for example, the rod tends to move slightly while the workpiece is subjected to repeated shaking.
An object of the present invention is to secure the operational reliability and increase the durability of a workpiece support by ensuring that fine shavings and the like do not penetrate into the apparatus from the small gap between the rod and the scraper.